The invention relates to a monitoring system for sampling and analyzing gas in a gas stream. The invention more particularly relates to a system for continuously monitoring the gaseous components of a gas stream wherein analysis of the gas is conducted at a convenient location that may be remote from the point where the gas sample is taken.
In many processes, it is desirable to regularly analyze the products of combustion or the products of other reactions to determine the efficiency of the reaction and to monitor what effluents are being exhausted from the reactions. Government regulations often require periodic or continuous monitoring of gases exhausted from manufacturing or combustion processes. Monitoring and analyzing exhaust gases is complicated by the requirement that samples of the exhaust gas often must be taken from flue stacks shortly before the exhaust gas is expelled to the atmosphere. On the other hand, gas analysis is generally most conveniently conducted in an enclosed, climate-controlled structure on the ground. The distance between sample taking and analysis is especially troublesome when stack gases must be monitored near the outlet of a flue gas stacks that are hundreds of feet tall.
The distance between gas sampling locations and gas analysis locations has resulted in a variety prior art gas monitoring systems. In early monitoring systems, gas analysis equipment was housed at a convenient location on the ground and samples were periodically taken from a probe in the flue gas stack and physically carried to the analysis site. However, transporting samples is inconvenient and often dangerous. In addition, it is desirable in many processes to continuously monitor the components of a gas stream. Indeed, certain government regulations require continuous monitoring of exhaust gas streams.
In order to achieve continuous and convenient gas monitoring, stack sample probes have been connected to gas analysis equipment through long sample lines. In such systems, a pump near the gas analysis equipment creates a suction in the long sample line that pulls gas into the sample probe and down the sample line to the pump whose outlet discharges sampled gas to the gas analysis equipment. Continuous monitoring systems with long sample transport lines introduce a number of gas monitoring inaccuracies. For example, when a heated gas sample taken from the flue stack is carried the length of a long sample transport line, the sample cools and liquid vapor in the sample condenses in the sample transport line. This condensed liquid gathers on the walls of the transport line and collects at low points along the transport line. When a liquid condensate forms in the sample transport line, the condensed liquids absorb contaminants passing through the gas line. The absorbed gas contaminants will not be detected by the analysis equipment at the time the gas contaminants are sampled. In addition, the condensate may later emit the absorbed gases or the condensate may react with a later gas sample resulting in additional inaccuracies. Thus, once liquid forms in the sample transport line, accurate gas monitoring becomes impossible.
To overcome the problem of condensation formation in the gas transport line, prior art systems insulated and heated the sample transport line such that the sample gas was kept heated between the sampling point and the gas analyzer. This heating was designed to prevent condensation in the transport line. However, gas transport line heaters periodically break down. After such breakdowns are discovered, it is necessary to turn off the monitoring system and clean condensate out the gas transport line. This maintenance is both expensive and time consuming.
One approach to overcoming the problems associated with long sample transport lines has been to move the gas analyzer to a location close to the gas sampling probe. In such systems, the gas analyzer is mounted on the flue gas stack near the sample probe and the analysis results are transmitted over electrical wires to a convenient location where the results are printed out on a terminal. Unfortunately, many gas analyzers are too large or too sensitive to be mounted on a flue gas stack and regular maintenance and calibration of gas analyzers is made inconvenient by locating analyzers on the flue gas stack.
Another problem associated with long sample transport lines in prior art monitoring systems is that the gas samples are pulled from the sample probe to the analyzer under suction. If there are any leaks in the long sample transport line, this suction pulls contaminants into the sample.